Unique expression of gonadotropin-I and -II subunit genes in male and female red seabream (Pagrus major) during sexual maturation

Two distinct gonadotropins (GTHs) have been demonstrated in a number of tel eost fishes. Although the physiological roles of GTHs have been extensively studied in salmonids, little is known about their biological functions in nonsalmonid fishes. In this study, to elucidate the role of GTH-I and GTH-I I in reproduction, we cloned the alpha-glycoprotein subunit (alpha GSU) and gonadotropin beta subunits (I beta and II beta) of red seabream using the 5'- and 3'-RACE methods and used these cDNA probes to reveal changes in mRN A levels of each subunit during sexual maturation of both male and female r ed seabream. The nucleotide sequences of alpha GSU, I beta, and II beta are 629, 531, and 557 base pairs long, encoding peptides of 117, 120, and 146 amino acids, respectively. The deduced amino acid sequence of each mature s ubunit showed high homology with those of other teleosts. Northern blot ana lysis showed that I beta mRNA levels of males increase in association with gonadal development, whereas those of females remain low throughout sexual maturation, indicating sexual dimorphism in the expression pattern of I bet a. In contrast, II beta mRNA levels of both sexes are maintained at high le vels from the beginning of gametogenesis to spawning season. These results are different than those of salmonids and suggest that GTH-I may have impor tant roles in male, but not female, gametogenesis. GTH-II may be involved i n regulation of early and late gametogenesis in both male and female red se abream.